Diagnosing 2jz-gte overheating

[Draven]

So, tonight my supra decided to overheat a bit.

Driving back from the pub, all was good initially, then suddenly it got to operating temperature very quickly (much quicker than usual)

On the way home, it would get up to 3/4 max temp (usually sits just below half, has never moved no matter what I've done to it). then it would suddenly drop back to just below half (take a few seconds to get back to this level)... then after 10-20 secs at usual temp it would creep back up to 3/4 over 10 secs or so, then drop back again.
At idle (lights) it crept up to 2/3rd max temp, then sat there and didn't move

My current guess is a sticking thermostat.. ie, replace with TRD item... any other suggestions?

kms are probably at 80K kms, so not quite due for a water pump replacement (although I'll probably end up doing taht at the same time). Could it be a temp sender issue?

[Alchemist]

When was the last time you flushed out your radiator? Got mine done at 100K service and mechanic said the sh!te that came outa there was quite impressive, obviously hadn't been loved previously.

TRD thermostat will certainly keep your engine cooler, but I don't think that's the immediate problem(unless your current stock thermostat has died).

Like you my 2J, no matter how hot or hard I've driven it has gone above 1/2.

Can't remember are the TT's thermofans or clutch? If thermos are they kicking in when stationary?

[thechuckster]

radiator cap?

[allencr]

it would suddenly drop back to just below half (take a few seconds to get back to this level)... then after 10-20 secs at usual temp it would creep back up to 3/4 over 10 secs or so, then drop back again.
replace with TRD item...
not quite due for a water pump replacement


Could it be a temp sender issue?

Sure it could & after having shown rapid temp swings that seem way too fast for any thermostat to affect and more then most electric gauges are capable of & assuming that the water pump failure would be 1 in a billion, the sender/gauge/wiring could definitly do it..

What's the real temp, with kitchen/whatever thermo.?
Do the core tubes look completely free or clogged inside the rad.? Same with the fins outside?
Is this 'trd' thing something special? The low temp thing they shill isn't & will not lower your temp., because it only controls the lowest temp. of the cooling system by when it opens, and will not do anything at all for anything higher then that & the highest temp. that your cooling system will get up to isn't going to be affected.

[1jz68u]

my mates aristo did that, you dont want to know the outcome.

as above try radiator cap. listen to see if the coolant is boiling when you stop.

i hope its something simple for you...

[Draven]

to clear it up - the TRD replacement is something I was always going to do when it was time to change thermostat/water pump - not related to trying to fix this problem (exceopt is current thermostat is broken)

I'm assuming Glenn that the other option is BHG

[IN 05 NT]

coolant low?....as that can cause the gauge to wander up and down as pockets of air/coolant pass by it,

pressure test system/check for leaks,

[big_zop]

Have you got acces to an aftermarket water temp gauge or a thermocouple you can stick into the system somewhere, under a clamp so oyu wont need an adaptor? Wont be able to tell you much since the factory gauge is just an indicator, not an absolute value. But at least you will be able to see what the water temp is really doing.

My car (although with over 200K kms) had an oil leak that caused the factory gauge to jump around, nothing like what you described - it would flicker its way down and come back up to the right spot. Also, how were you driving when you noticed the gauge moving as the other thing my car did after the radiator was cleared after a BHG was that at 100% throttle it would drop steadily till i had to lift to change gears, could be from cavitation (air causing the gauge not to read correctly) or sudden flow of colder water. But again, it would return to normal operating temp.

Also, a TK (sp?) test will be able to tell you if the HG is blown and there is exhaust gas present in the water, but not if its about to go though.

[Draven]

I'm going to start with the simple and progress toward the expensive

I had a looksee today in daylight, no oil in water, no water in oil (that I could see)... this is a good thing (but doesn't totally rule out BHG).

First thing to do will to be absolutely sure I've got tons of water/coolant in the system and see what happens. overflow bottle still has plenty in it, but maybe it's not sucking back in.

rad cap looks in pretty good condition - no perishing, etc.

Anyone have a spare temp reader they'd like to let me borrow?

[1jz68u]

i have an oldish VDO guage just sitting here

[Draven]

with sender? it's not the guage I'm terribly worried about

[oldcorollas]

On the way home, it would get up to 3/4 max temp (usually sits just below half, has never moved no matter what I've done to it). then it would suddenly drop back to just below half (take a few seconds to get back to this level)... then after 10-20 secs at usual temp it would creep back up to 3/4 over 10 secs or so, then drop back again.
At idle (lights) it crept up to 2/3rd max temp, then sat there and didn't move

My current guess is a sticking thermostat.. ie, replace with TRD item... any other suggestions?

does your temp gauge respond quickly? (VDO like?)

i would see same cycle when warming up, whe the hole in thermostat was too small.. but this was not overheating tho..

what i mean is.. that behaviour sounds like normal operation of thermostat, but the temp might be wrong if the thermostat is farked...

drill a 2mm hole in next stat to allow water to pass thru and reduce the fluctuations?

plus all the more expensive fixes...

[1jz68u]

with sender? it's not the guage I'm terribly worried about

sure does, it has a little dent in it. its not pretty but it definitely works.

its a mechanical one.

[Draven]

turns out rad could take a decent bit of water. once I sober up, I'll take her for a little squirt and see what happens

[131OWN]

If you have no visible water leaks, I would perform a leakdown test to determine if the headgasket is blown.